Here, user_id would be the person who cast the vote, polarity would be either '1' for an upvote or '-1' for a downvote (this lets you just sum the polarities to get upvotes and downvotes to cancel), votable_type would contain what the vote is for (Post or Comment), votable_id would contain the id of the thing the vote is for, and total would keep a running total of the vote sum (for efficiency).